﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;

namespace Service.ZSJL.Com.Utils
{
   
        public static class QueryExtensions
        {
            /// <summary>
            /// Linq排序扩展方法
            /// </summary>
            /// <typeparam name="T"></typeparam>
            /// <param name="source"></param>
            /// <param name="propertyName">属性的字符串名称</param>
            /// <param name="sort">方向</param>
            /// <returns></returns>
            public static IQueryable<T> SortBy<T>(this IQueryable<T> source, string propertyName, SortDirectionEnum sort)
            {
                if (source == null)
                {
                    throw new ArgumentNullException("source");
                }

                if (String.IsNullOrEmpty(propertyName) || propertyName.Trim().Length == 0)
                {
                    return source;
                }

                ParameterExpression parameter = Expression.Parameter(source.ElementType, String.Empty);
                MemberExpression property = Expression.Property(parameter, propertyName);
                LambdaExpression lambda = Expression.Lambda(property, parameter);

                string methodName = (sort == SortDirectionEnum.Ascending) ? "OrderBy" : "OrderByDescending";

                Expression methodCallExpression = Expression.Call(typeof(Queryable), methodName,
                                                    new Type[] { source.ElementType, property.Type },
                                                    source.Expression, Expression.Quote(lambda));

                return source.Provider.CreateQuery<T>(methodCallExpression);

            }

        }

        /// <summary>
        /// 指定对项列表进行排序的方向。
        /// </summary>
        public enum SortDirectionEnum
        {
            /// <summary>
            /// 从小到大排序。例如，从 A 到 Z。
            /// </summary>
            Ascending = 0,
            /// <summary>
            /// 从大到小排序。例如，从 Z 到 A。
            /// </summary>
            Descending = 1,
        }
    
}
